Method for reducing the number of pins required for an interface to an electronic device and devices using the method

ABSTRACT

A single signal trace can be multiplexed between a circuit that provides a reference voltage and another circuit that is not operational while the reference voltage is needed. Fewer signal connections will be needed due to the multiplexing. As one possible example, a clock signal that is used at initial power up of an electrical circuit can later be used as a reference voltage. In one specific example, a signal line is connected from one electronic device to a second electronic device. The signal line is connected to a clock input of a circuit and an input to an amplifier. When the devices first power up a clock signal is active on the signal line and is used to the clock input. When the clock signal is no longer needed the signal can be used to drive the amplifier to create a reference voltage.

1. FIELD

The invention generally relates to electronic devices and moreparticularly relates to interconnections between electronic devices.

2. BACKGROUND

Electronic devices have become almost ubiquitous in many parts of theworld. Computers, televisions, and stereos are common in many areas.Additionally, mobile electronic devices are also becoming more common,including portable computers, portable stereos, and portabletelevisions. Mobile handsets, sometimes referred to as mobile phones areanother example of the multitude of different electronic devicesavailable.

Many electronic devices have other external electronic devices attachedto them. One example is a mobile wireless device with a hands-free carkit attached. A hands-free car kit is a device that allows a mobilehandset user to talk during a mobile call without having to hold themobile handset near the user's head.

When connecting one electronic device to another, in many cases, isadvantageous to minimize the number of connections between the devices.To illustrate, an example of a mobile handset and a hands-free car kitwill be discussed, however, it will be clear that other examples arepossible. Many mobile electronic devices can benefit by decreasing thenumber of connections between each mobile electronic device.Additionally, other examples of electronic devices that are not portableare possible.

Now, returning to the specific example, a mobile handset and ahands-free car kit is described. As stated above, the cost of connectorscan, in some cases increase when the number of connections increases.Additionally, connectors with more connections are typically larger thana similarly constructed connector with fewer pins. For these reasons itmay generally be advantageous to decrease the number of connectionsbetween two electronic devices.

Another problem with electronic devices is that in some cases noise canbe caused by the amount of current that flows between two devices. Thecurrent flow is in some cases variable. This variable current can causesignal levels in the devices to vary. As a specific example, when onedevice provides power to a second device the voltage level of a groundreference may vary due to the changing current in the conductorconnecting the two devices. In many cases noise can adversely effect theperformance of electronic devices. One specific example is when a signalis an audio signal. Noise coupled onto an audio signal can be readilyapparent to the user of an electronic device in many cases.Specifically, when the noise coupled to an audio signal creates audiblenoise to output from a speaker, the noise adversely effects theperformance of the mobile handset for the user.

It would generally be advantageous to find a way to lower the signalcount on the connectors of an electronic device. It would also generallybe advantageous to limit noise coupling onto signal lines. Generally,limiting noise coupling onto signal lines while also lowering signalcount may lower cost and improve the performance of electronic devices.

3. SUMMARY

In some cases electronic devices are connected to other electronicdevices. In some cases the two electronic devices may be a mobilehandset and a hands-free car kit or other mobile handset accessory.Other examples are possible, for example, the two electronic devices maybe a computer and an external computer peripheral. In many cases thenumber of connections between the two electronic devices is limited. Theexpense associated with the connectors and cable used to connect the twodevices may increase as the number of electrical connections increases.Additionally, the size of the connector may increase as the number ofconnections increases. Alternatively, connectors may be similar in size,but one with more connections may tend to be more expensive, or harderto manufacture. In many cases, a way of multiplexing multiple signals ona single conductor would tend to be advantageous. Note that the aboveexamples, are only intended to be examples, other examples are possible.Other reasons may exist for multiplexing multiple signals on a singleconductor.

Some electronic devices, such as mobile telephone handsets and mobiletelephone handset peripherals may include audio signals. In some casesaudio signals may be especially susceptible to noise. The noise may beaudible to the user. Typically, users of electronic devices, such asmobile telephone handsets do not like to hear noise. Noise tends tointerfere with telephone conversation. It would be advantageous todecrease noise in electrical circuits, especially, in some cases,electrical circuits that contain audio.

If a single signal trace is multiplexed between a circuit that providesa reference voltage and another circuit that is not operational whilethe reference voltage is needed fewer signal connections will be needed.As one possible example, a clock signal that is used at initial power upof an electrical circuit can later be used as a reference voltage. Inone specific example, a signal line is connected from one electronicdevice to a second electronic device. The signal line is connected to aclock input of a circuit and an input to an amplifier. When the devicesfirst powers up a clock signal is active on the signal line and is usedto drive the clock input. When the clock signal is no longer needed thesignal can be used to drive the amplifier to create a reference voltage.

Advantages may in some cases include lowering pin count on connectorsused to connect two electronic devices. The size of a connector may alsobe reduced, additionally, in some cases, the cost of the connector maybe reduced. Other advantages may include lower noise in an electricalcircuit. Additionally, this may lead to lower noise in an audio circuit.Not all advantages, however, will occur in every implementation. As anexample, in an electronic device that does not have audio, loweringaudio noise would not be an advantage for that device. The device mayhave other advantages either related to noise reduction in an electricalcircuit, or not related to noise reduction.

Generally, as would typically be the case with the mobile handsetexample, one device will often be contained within one case, and theaccessory will often be contained in another case. In this example,typically a cable connects the two devices and the number of connectionsbetween the device can be lowered by using the method. It will be clear,however, that the method could be applied to other examples. As anadditional example, the method could be used to limit the number ofconnections in a set of connectors between multiple boards in anelectronic device. The method could also be used to limit the number ofsignal traces on a printed wire board.

The method and devices multiplex multiple signals on a single signalline. In a specific example, an audio reference is generated bymultiplexing an external voltage and a clock signal into a digitalinterface that does not have a usable, clean common reference signal. Inthe specific example the audio is muted when the digital communicationoccurs.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram, showing a mobile communication device accessory

FIG. 2 is a diagram showing a mobile communication device connected to amobile communication device accessory.

FIG. 3 is an example of a mobile communication device accessory.

FIG. 4 is an example of two circuit boards stacked together implementingan embodiment.

5. DETAILED DESCRIPTION

Referring now to FIG. 1, a diagram of a mobile communication deviceaccessory 100 is shown. The mobile communication device accessoryincludes a case 105. The case is shown enclosing several othercomponents. It will be clear that this is only one possible example. Theactual components that are enclosed in the case in any particularimplementation may vary, and the scope should only be limited by theclaims.

Referring back to FIG. 1, the case 105 has, as an input, a signal line113. The signal line 113 is connected, through a switch 115 to a firstcircuit 110 and to a second circuit 120. The switch 115 allows thesignal line to be connected and disconnected from the first circuit 110.Additionally, the signal line 113 provides an input voltage 131 to thefirst circuit 110 when the switch is closed.

The first circuit 110 outputs a reference voltage 127 that is typicallya function of the input voltage 131. The reference voltage is in manycases used within the mobile communication device and may be the same,or similar in voltage level to a ground line. In many cases, the firstcircuit is a high impedance follower circuit.

A switch control 130 is used to control the connection between thesignal line 113 and the first circuit. It will be clear that in somecases, the diagram shown in FIG. 1 may be a simplified version. Otherimplementations are possible. Again, the scope should only be limited bythe claims. An advantage in some cases, may be the ability to use asingle signal line to drive multiple circuits. FIG. 1 shows an exampleof a mobile communication device, however, this is only one possibleexample. The device could be any electronic device accessory. It willalso be clear that an electronic device accessory is typically anelectronic device.

An advantage is that the reference voltage 127 shown in FIG. 1 may tendto be less noisy than a reference voltage that is supplied directly froman external mobile communication device, or other external electronicdevice. The first circuit is typically a high impedance, low currentdevice. For this reason, the noise on the signal line 113 wouldtypically be low. Additionally, the reference voltage output from thefirst circuit 110 would typically be near the circuitry using thereference voltage, lowering the noise generated by currents flowing overlong signal paths. It should, however, be noted that this is only ageneralization, and may not apply to all implementations.

FIG. 2 is a diagram 200 showing a mobile communication device 204connected the mobile communication device accessory 100 of FIG. 1. Thediagram 200 shows one possible implementation. Other implementations arepossible. The signal line 113 couples an external voltage 202 from themobile communication device to the mobile communication device accessory100 of FIG. 1.

Again, while a mobile communication device 204 and a mobilecommunication device accessory 100 are shown, it will be clear thatother combinations of electronic devices are possible. As FIG. 2illustrates, by using a single signal line 113, multiple circuits 110,120 can be driven.

In some cases only one circuit is driven at a time. For example, thesecond circuit 120 may be a digital circuit that requires a clock. Inthis example, the digital circuit is only required to operate when thedevice first powers up. Additionally, the first circuit 110 may providea ground reference for analog circuitry that is only used after thedevice first powers up and the digital circuitry is no longer needed.

As a more specific example, suppose that the mobile communication deviceaccessory 100 is a hands free car kit. A hands free car kit is a devicethat connects to a mobile telephone handset and allows a user to conducta mobile telephone call while minimizing the user's interaction with themobile telephone handset. For example, hands free car kits typicallycontain a microphone that picks up the users voice without requiring theuser to hold the microphone near the users mouth. In some forms themicrophone may be held near the users mouth by a clip, however, in otherforms the microphone may be constructed so that it is not required to benear the users mouth.

The hands free car kit may contain a memory device. The second circuit120 may be that memory device. The memory device contains informationthat is clocked out of the device during a first time period, typicallythe initial stage of powering up. After the information has been clockedout of the memory device, the clock signal is no longer needed, and thefunctionality of the memory device is no longer needed. During thissecond time period the line that the clock signal was on may be used forother purposes.

As an example, the hands free car kit may contain a speaker that allowsthe user to hear a mobile telephone call. The sound quality of the soundthat comes from the speaker and the circuitry that drives the speakermay be improved if a clean reference voltage is provided to the speakerand circuitry. After the memory device is no longer needed, the clocksignal can be driven to a low voltage and used as an input to the firstcircuit 110. The first circuit 110 can be used to provide a referencevoltage 127 to the speaker and the circuitry that drives the speaker.

This is only one possible example. It is intended to illustrate onepossible use for some of the embodiments described in this application.Other embodiments are possible.

FIG. 3 is an example of a mobile communication device accessory 250. Themobile communication device is similar to the mobile communicationdevice 100 described with respect to FIGS. 1 and 2. The mobilecommunication device 250 includes a signal line 253. The signal line 253is the same or similar to the signal line 113 of FIGS. 1 and 2. Thesignal line 253 is coupled to other circuitry through a resistor 256.The resistor 256 may not be used in every implementation. It will beclear, however, that most signal lines have some resistance. Noteresistor was not shown in FIGS. 1 and 2. Recall that FIGS. 1 and 2 areintended to generally detail a possible implementation and that otherimplementations are possible. The scope should only be limited by theclaims.

A switch in the form of a transistor 263 is shown on FIG. 3. Thetransistor 263 is one possible implementation of the switch 115 shown onFIGS. 1 and 2. The transistor is controlled by a signal 266 that isconnected to the switch control. The switch control is not shown in FIG.3, however, it is the same or similar to the switch control 130 of FIGS.1 and 2.

An amplifier, in the form of an operational amplifier 268 is shown inFIG. 3. The operational amplifier is shown as a “follower” circuit. The“follower” circuit tends to output a signal that closely follows thevoltage on signal line 253. This is intended to be a general statementregarding the typically functioning of a “follower” circuit. It will beclear that in some cases the “follower” circuit may not output a voltagethat is close to the input voltage.

As shown in FIG. 3 the operational amplifier 268 circuit will typicallybe provided an input near ground. The input is provided through thetransistor 263. The operation amplifier 268 will typically output avoltage that is near ground and can be used as a reference voltage 270.The reference voltage 270 is the same or similar to the referencevoltage 127 of FIGS. 1 and 2. Additionally, the operational amplifier isone possible implementation of the first circuit 110 of FIGS. 1 and 2. Asecond circuit 259 is shown on FIG. 3. The second circuit 259 is thesame or similar to the second circuit 120 of FIGS. 1 and 2. FIG. 3 isintended to show one possible implementation. Other implementations arepossible.

Referring now to FIG. 4, another example will be discussed. In thisexample a connection is made between two circuit boards. In the examplesdiscussed with respect to FIGS. 1, 2, and 3 a connection is typicallymade between two circuit boards. In these examples the signal line 113is used to make the connection. Similarly, connections are made betweentwo circuit boards 355, 360 in FIG. 4.

FIG. 4 is a diagram 350 that depicts two circuit boards 355, 360 stackedtogether. The two circuit boards 355, 360 are mechanically connected totwo metal pieces 358, 367 that position the circuit boards 355, 360relative to each other. This is only one possible mechanical assembly.In many cases no metal pieces 358, 367 are required. Additionally, insome cases the metal pieces 358, 367 may be made of a material otherthan metal. The example is only intended to be illustrative. Thecircuits described may be used in many different devices and mechanicalassemblies. For example, while two circuit boards 355, 360 are shown inFIG. 4, additional circuit boards are possible.

FIG. 4 includes two connectors 372, 374. The connectors connectelectrical signal traces from the top circuit board 355 to the bottomcircuit board 360. The connectors 355, 360 may typically connectmultiple signal traces, however, in some cases, a single signal tracemay be connected by the connectors 272, 374. In many cases, the size ofthe connectors 372, 374 may be limited, and the number of electricalconnections may be limited. One advantage is that two different signals,for example, as discussed above, a clock and a ground reference aremultiplexed and only require a single electrical connection.

It will be understood that the same or similar circuits discussed withrespect to FIGS. 1, 2, and 3 are placed on the circuit boards 355, 360.The circuits may be similar in form, function, or both. Typically, onecircuit board 355 will have the circuit discussed with respect to themobile communication accessory 100 of FIG. 2 and the other circuit board360 will have the circuit discussed with respect to the mobilecommunication device 204. It will also be understood that the placementof the circuits on the top or bottom board could be swapped.Additionally, as stated above, more than two boards are possible.

Several examples have been discussed, however, as stated above, theseare only possible examples, other examples will occur to one of skill inthe art. The scope should only be limited by the claims. Electricalcircuits can be designed in many different forms and still perform thesame or similar function. Additionally, electrical circuits that areinitially used in one specific device or devices can, in many cases, beused in many different devices. In different specific implementationsthe same or similar circuits may have the same advantages, however, acircuit may not have every advantage discussed in every implementation.

1. A mobile communication device accessory comprising: a first circuitconfigured to output a reference voltage based on an input voltage; aswitch coupled to the first circuit and configured to connect anexternal voltage to the circuit; a switch control coupled to the switchand configured to control the switch; a signal line connected to theswitch and configured to couple and de-couple the first circuit to theexternal voltage; wherein the signal line is coupled to a second circuitand configured to couple the second circuit to the external device whenthe first circuit is de-coupled from the external voltage; a caseenclosing the first circuit.
 2. The mobile communication deviceaccessory of claim 1 wherein the second circuit is not coupled to theexternal device when the first circuit is coupled to the externaldevice.
 3. The mobile communication device accessory of claim 1 whereinthe first circuit includes an amplifier.
 4. The mobile communicationdevice accessory of claim 3 wherein the amplifier is an operationalamplifier.
 5. The mobile communication device accessory of claim 4wherein the operational amplifier is configured as a follower circuit.6. The mobile communication device accessory of claim 1 wherein thereference voltage is a ground reference.
 7. The mobile communicationdevice accessory of claim 1 wherein the reference voltage is within 0.5volts of power ground.
 8. The mobile communication device accessory ofclaim 1 wherein the reference voltage is within 1.0 volts of powerground.
 9. The mobile communication device accessory of claim 1 whereinthe switch is a transistor.
 10. The mobile communication deviceaccessory of claim 9 wherein the transistor is a field effecttransistor.
 11. The mobile communication device accessory of claim 1wherein the switch control is a mute control line configured to causethe switch to connect the signal line to the first circuit when soundoutput from the accessory is not muted.
 12. The mobile communicationdevice accessory of claim 1 wherein the signal line is multiplexed. 13.The mobile communication device of claim 1 wherein the signal line is aclock signal line during a first time period of operation and is drivento a low voltage during a second time period.
 14. The mobilecommunication device of claim 1 wherein the external voltage is used togenerate an audio reference voltage.
 15. A mobile communication deviceand accessory combination comprising: a first circuit configured tooutput a reference voltage based on an input voltage; a switch coupledto the first circuit and configured to connect an external voltage tothe circuit; a switch control coupled to the switch and configured tocontrol the switch; a signal line connected to the switch and configuredto couple the first circuit to the external voltage; wherein the signalline is coupled to a second circuit and configured to couple the secondcircuit to the external device when the first circuit is de-coupled fromthe external voltage; a case enclosing the first circuit.
 16. The mobilecommunication device accessory of claim 15 wherein the first circuitincludes an amplifier.
 17. The mobile communication device accessory ofclaim 16 wherein the amplifier is an operational amplifier.
 18. Themobile communication device accessory of claim 17 wherein theoperational amplifier is configured as a follower circuit.
 19. Themobile communication device accessory of claim 15 wherein the referencevoltage is a ground reference.
 20. The mobile communication deviceaccessory of claim 15 wherein the reference voltage is within 0.5 voltsof power ground.
 21. The mobile communication device accessory of claim15 wherein the reference voltage is within 1.0 volts of power ground.22. The mobile communication device accessory of claim 15 wherein theswitch is a transistor.
 23. The mobile communication device accessory ofclaim 22 wherein the transistor is a field effect transistor.
 24. Themobile communication device accessory of claim 15 wherein the switchcontrol is a mute control line configured to cause the switch to connectthe signal line to the first circuit when sound output from theaccessory is not muted.
 25. The mobile communication device accessory ofclaim 15 wherein the second circuit is not coupled to the externaldevice when the first circuit is coupled to the external device.
 26. Anelectronic device accessory comprising: a first circuit configured tooutput a reference voltage based on an input voltage; a switch coupledto the first circuit and configured to connect an external voltage tothe circuit; a switch control coupled to the switch and configured tocontrol the switch; a signal line connected to the switch and configuredto couple the circuit to the external voltage; wherein the signal lineis coupled to a second circuit and configured to couple the secondcircuit to the external device when the first circuit is de-coupled fromthe external voltage; a case enclosing the first circuit.
 27. A methodof connecting a first electronic device to a second electronic devicecomprising the steps of: connecting the first device to the seconddevice using a conductor; configuring a first circuit to output areference voltage based on an input signal transmitted across theconductor during a period of time; configuring a switch to couple thefirst circuit to the input signal during the time period; adapting aswitch control to control the switch; configuring the signal line toconnect the conductor to a second circuit when the first circuit isde-coupled from the external voltage;
 28. The method of claim 27 whereinthe second circuit is not coupled to the external device when the firstcircuit is coupled to the external device.
 29. The method of claim 27wherein the first device is a mobile communication device.
 30. Themethod of claim 27 wherein the second device is a mobile communicationdevice accessory.
 31. The method of claim 27 wherein the switch used isa transistor.
 32. The method of claim 27 wherein an amplifier is usedfor the first circuit.
 33. The method of claim 32 including the step ofconfiguring an operational amplifier to output a reference voltage. 34.The method of claim 27 wherein the reference voltage is an audioreference.
 35. The method of claim 34 wherein an audio signal is mutedwhen the first circuit is decoupled from the external voltage.